The present invention relates generally to an apparatus for detecting markings on a wood block. The block has been formed previously on the opposite end faces thereof with markings the centers of which define an axis about which the block should be rotated for achieving maximum yield in peeling veneer from the block in a rotary veneer lathe. Therefore, the invention relates more specifically to an apparatus for detecting such markings and positioning the block on the basis of marking detection data such that the axis of the block is set parallel to the axes of spindles of the veneer lathe.
In peeling veneer from a rotating log or wood block, it is desirable that the block should be rotated about an axis that permits maximum veneer yield. For this purpose, it has been a practice in many veneer mills to determine its optimum axis by using mechanical, optical or any other suitable centering apparatus and then to mark the centers on opposite end faces of the block, i.e. the points at which the optimum axis intersects the respective block end faces. Markings may be provided by any suitable means, for example, by painting or drilling a hole representing such center, as proposed by Publication of Japanese examined patent application H4-31847. In transferring the block to a rotary veneer lathe, the markings are detected and the block is moved to a predetermined position in the veneer lathe where the optimum axis of the block coincide with the rotational axes of the respective spindles of veneer lathe.
The present inventor attempted to locate the markings by using an apparatus as provided schematically in FIG. 27 showing the apparatus in side view and FIG. 28 showing the same apparatus in plan view. The apparatus include a pair of image sensors such as CCD (charge coupled device) cameras 205, 205 each having a lens and an image pickup device, or CCD, on which an image covering part of block end face passed through the lens is produced. The CCD cameras 205, 205 are disposed opposite to one another so as to face the opposite end faces 201a, 201a of a block 201 which is placed on a pair of V-shaped supports 203, 203 between the cameras. The block supports 203, 203 are movable independently of one another in vertical and horizontal directions as indicated by double-head arrows. The block 201 is previously formed at the center of its opposite end faces 201a, 201a with drilled holes 201b, 201b as markings. Though not shown, the apparatus further includes an image processing unit and a computer control.
In operation, light is emitted at an angle against each end face 201a of the block 201 so that the hole 201b appears as a shaded area while the remaining surface as lighted area. Light reflected from the end face 201a and passed through the lens creates on CCD an image of central portion of the end face 201a with image of the hole 201b appearing as a black circular dot. Information or binarized data of object image is sent to the image processing unit, which then determines the position or displacement of each circular dot with respect to a predetermined reference or zero point on CCD and generates electrical signals representing such displacement. Receiving the signals from the image processing unit, the control generates electrical signals which cause the respective block supports 203, 203 to move independently such that the circular dots may be relocated on the zero points of CCDs, i.e. the centers of respective markings 201b, 201b on the opposite block end faces 201a, 201a may be positioned on an imaginary line passing through the zero points of CCDs.
Subsequently, the block 201 is clamped at its opposite ends by a pair of holders (not shown) and then transferred to a rotary veneer lathe (not shown) so that the block 201 may be loaded in the veneer lathe with the center markings 201b, 201b positioned in alignment with the axes of the lathe spindles.
The inventor noted through experimental operation of the apparatus that, if the apparatus uses CCD camera 205 with a lens whose focal length is relatively large, its high resolution capability makes possible accurate detection of the marking 201b, while the area of image to be produced on CCD is narrowed with the result that image of the marking 201b may not fall within the image pickup area of CCD and, therefore, failure in marking detection may occur. If a lens with a relatively short focal length is used, on the other hand, the area of image is enlarged, but accurate detection cannot be accomplished because of poor resolution of the lens. As a result, block 201 when placed in the veneer lathe maybe off-centered with respect to the axes of lathe spindles over a range from a few millimeters to more than ten millimeters. In view of the fact that in many veneer mills wood blocks are being peeled to produce thin sheets of veneer, say about 0.6 mm, the above error will seriously affect the resulting veneer yield.
Therefore, an object of the present invention is to solve the above problems by improving the apparatus which the present inventor used in an attempt to detect the center markings on a peeler block.
More specifically, the present invention is directed to provide an apparatus which detects the markings on a block at least at a first rough detecting stations and a second fine detecting station so that the block is finally positioned with its optimum axis set in parallel with the axes of spindles of a rotary veneer lathe, thereby making it possible in the subsequent process to transfer the block and load the veneer lathe with the block such that its optimum axis coincides with the rotational axes of the veneer lathe spindles.
In order to achieve these objects, the invention contemplates an apparatus for detecting markings on the opposite end faces of a wood block, which comprises a pair of movable support members for supporting the block in such orientation that the axial length of the block extends across the direction in which said support members are moved, and drive means for independently and controllably moving the support members. In the preferred embodiment of the invention, the block is detected at the first and second stations and then moved a third position where the block is finally positioned ready to be transferred to a rotary veneer lathe. For detecting the markings, the apparatus further includes first and second pairs of image sensor means. The image sensor means of the first pair have lenses disposed so as to face the opposite end faces of the block positioned at the first detecting station and image pickup devices on which images of the markings through the lenses thereof are produced, while the second paired image sensor means have lenses disposed so as to face the end faces of the block which is positioned at the second detecting station and similar image pickup devices. The lenses of the first paired image sensor means has a focal length which is smaller than that of the lenses of the second paired image sensor means. In the preferred embodiment, the focal length of the lenses of the first paired image sensor means is 16 mm against 50 mm for the lenses of the second paired image sensor means.
Each image sensor means is connected to image processing means which is operable to determine the position or displacement of marking image produced on the image pickup device with respect to a predetermined reference point on the devices.
The apparatus further includes control means which receives information of the marking image displacement from the image processing means. Because of the relatively short focal length of lenses for the first paired image sensor means, and hence their wide-angle viewing capability, markings on the block end faces can fall well within the viewing area of the first paired image sensor means. Receiving from the image processing means the information of marking images on the image pickup devices of the first paired image sensor means, the control then computes the distances and the directions of movement of the respective support members necessary for the markings on the block at the first detecting station to move to positions corresponding to the reference points on the image pickup devices of the second paired image sensor means and generate signals which causes the drive means to move the support members independently for the computed distance in the computed direction toward the second detecting station.
The control means is also operable also to compute, on basis of information of the displacement of the marking images produced on the image pickup devices of the second paired image sensors means, the distances and the directions of movement of the respective support members necessary for the markings on the block at the second detecting station to move to predetermined positions at the third station and then to generate signals which causes said drive means to move said support members independently for the computed distance in the computed direction toward the third station. Because the lenses of the second paired image sensor means have a longer focal length and hence high resolution capability, the markings can be detected with higher accuracy at the second station and, therefore, the block is moved to the third station where its axis can be positioned accurately with respect to the axes of rotary veneer lathe spindles.
According to the preferred embodiment of the invention, the markings are provided by holes about 30 mm in diameter formed at the respective centers on the opposite end faces of the block, and the image sensor means includes a CCD camera having a charge coupled device (CCD) as the image pickup device.
It is desirable that the apparatus comprises drive mechanism for moving the image sensor means of each pair toward and away from each other according to the axial length of the block to be detected, i.e. the positions of the respective end faces of the block placed at the detecting stations.
In the preferred embodiment, the apparatus has a pair of parallel arm members supporting thereon the block support members for linear movement along such parallel members and independently pivotable about an axis adjacent to the first detecting station for angular movement. The movement of the block suppor members effected by the signal from the control means is accomplished by combination of the linear movement of the block support members and the angular movement of the parallel arm members.
Alternatively, the apparatus may have a pair of vertically movable parallel horizontal members supporting thereon the block support members, so that the support member are movable linearly along such parallel horizontal members and also may be raised with vertical movement of the parallel horizontal members. In the case of this embodiment, the movement of the supporting members effected by the signal from the control means is accomplished by combination of the horizontal linear movement of the block support members and the vertical movement of the parallel horizontal members.
In a further modified embodiment, the third station may be replaced by the second detecting station, so that, after the second detection of the markings at the second station, relocation of the markings may be performed at the same second station.
Features and advantages of the present invention will become more apparent to those skilled in the art from the following description of preferred embodiments according to the invention, which description is made with reference to the accompanying drawings, wherein: